Author Topic: How to amplify Super High Frequency signals?  (Read 5420 times)

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Offline Tantal

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How to amplify Super High Frequency signals?
« on: June 02, 2015, 08:28:32 am »
I'd like to amplify signals in the 5 GHz band. How would I do this? I assume I can not simply take a Darlington transistor, a LM386 Audio Power Amplifier or a LM2902 general purpose Op Amp, no?

With "amplify" I mean going from a few mW to something like 1 to 5 W.
 

Online daqq

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Re: How to amplify Super High Frequency signals?
« Reply #1 on: June 02, 2015, 08:39:14 am »
Well, there are specialized amplifier modules, but they are somewhat costly. Beyond a certain frequency you are entering the realm of microwave black magic.

https://www.hittite.com/products/index.html/category/241#
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Offline LukeW

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Re: How to amplify Super High Frequency signals?
« Reply #2 on: June 02, 2015, 10:11:38 am »
Here's an example of a MMIC (monlithic microwave integrated circuit) which is a 1W power amp designed for 5.8 GHz use.

http://www.minikits.com.au/doc/TC3531.pdf

This is a bit smaller than the power output you actually want, but it's just an example. Putting something like that on a PCB layout yourself requires understanding things like 50-ohm microstrip transmission lines, but there are boards you could get off-the-shelf to avoid having to do that yourself.

http://www.minikits.com.au/electronic-kits/rf-amplifiers/rf-high-power/6cm-1W-Amplifier

Say your power input is 3mW, or 4.77 dBm.

And you want a power output of 5W, or 37 dBm. So your gain needs to be about 32 dBm, plus whatever your cable/connector/etc losses are.

There's also an obvious lecture that could go here about your need to comply with any applicable RF transmission licensing/regulations in your country, but I'll skip it for the moment.

The above IC has a gain of 24 dB, so at 3mW in you'll get 0.75W out (4.77 dBm + 24 dB = 28.77 dB, so you can see why dB makes life easier.)
 

Offline Tantal

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Re: How to amplify Super High Frequency signals?
« Reply #3 on: June 02, 2015, 11:06:08 am »
Putting something like that on a PCB layout yourself requires understanding things like 50-ohm microstrip transmission lines, ...

Is this something like this? TL1, TL2 and TL3. And if so, what's the use of this "50-ohm microstrip transmission lines"
 

Offline dom0

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Re: How to amplify Super High Frequency signals?
« Reply #4 on: June 02, 2015, 11:47:03 am »
If you don't know what transmission lines are, then it will be an extremely long and painful process to get anything working at GHz frequencies. It is thus probably a much better idea to buy a finished amplifier module.

What do you need it for? There are usually special amplifiers for many applications, which are geared towards the applications' requirements.
,
 

Offline LukeW

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Re: How to amplify Super High Frequency signals?
« Reply #5 on: June 02, 2015, 12:07:06 pm »
The transmission lines (tracks on the PCB, if it's a PCB-based device) need to have the right impedance, the same as the source, the other cables, the inputs and outputs of the amplifier etc, otherwise there will be an impedance mismatch at that transition.

These lecture slides explain some of the basics, but I can't think of any good websites that go through it all in a nice beginner-friendly way.
https://www.jlab.org/accel/eecad/pdf/050rfdesign.pdf

Here are a couple of other examples of multi-watt RF amplifiers, a bit more powerful than the one I mentioned earlier. (Note that these devices can easily hit hundreds of dollars a piece.)

http://www.cree.com/~/media/Files/Cree/RF/Data%20Sheets/CMPA5585025F.pdf

http://cdn.macom.com/datasheets/MAAP-010169.pdf
 

Offline Tantal

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Re: How to amplify Super High Frequency signals?
« Reply #6 on: June 02, 2015, 02:14:03 pm »
If you don't know what transmission lines are, then it will be an extremely long and painful process to get anything working at GHz frequencies.

That doesn't matter. I'll take the time and I'm willing to learn.

Quote
What do you need it for? There are usually special amplifiers for many applications, which are geared towards the applications' requirements.

First a "simple" beacon, later a radar. But as I said: I know it takes a lot of time and reading. So first I'd like to be able to build a device that generates RF signals in that frequency range (>1GHz). Second amplify said signal.

As someone in another thread mentioned I should probably aim for 2.4GHz first, because there are a lot more affordable devices out there. Also spectrum analyzers >3GHz are way too expensive for me.

So let me reformulate my original question: How to amplify 2.4GHz signals from a few mW to 1 to 5 W?
 

Online PA0PBZ

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Offline Tantal

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Re: How to amplify Super High Frequency signals?
« Reply #8 on: June 02, 2015, 03:05:01 pm »
http://www.ebay.com/itm/2-4Ghz-5W-5000mW-Wireless-WiFi-Amplifier-LAN-Broadband-Router-Signal-Booster-/161427987945

Thank you for the link, but I don't want to simply buy a ready-made device from eBay. I'd like to learn how to build such devices myself.

The interesting question (for me) is: What's in that box? How does it work? Which components does it use?
 


Offline Mechatrommer

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Re: How to amplify Super High Frequency signals?
« Reply #10 on: June 02, 2015, 04:59:50 pm »
If you don't know what transmission lines are, then it will be an extremely long and painful process to get anything working at GHz frequencies.
That doesn't matter. I'll take the time and I'm willing to learn.
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Online T3sl4co1l

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Re: How to amplify Super High Frequency signals?
« Reply #11 on: June 02, 2015, 05:40:53 pm »
You might be better off starting with a novelty such as a microwave oscillator or Gunn diode in a cavity resonator.

Keep the output power well under 1W, more is illegal.  Especially if you'll be using crunchy amplifiers that throw out harmonic distortion, and oscillators with poor tracking (the 2.4GHz ISM band is only so many percent wide).

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Offline awallin

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Re: How to amplify Super High Frequency signals?
« Reply #12 on: June 02, 2015, 06:46:28 pm »
There are a couple of DIY designs for GHz prescalers for frequency counters. These might be good example circuits/PCBs for you to look at:

For example:
http://gerrysweeney.com/diy-hpagilent-53131a-030-3ghz-channel-3-option-board/
(there are many others, google for 'diy prescaler' or 'microwave frequency counter option' or similar)
 

Offline jpb

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Re: How to amplify Super High Frequency signals?
« Reply #13 on: June 02, 2015, 07:57:17 pm »
My first job on graduation (and many years subsequently) was with monolithic microwave integrated circuit research (GaAs). 5GHz is actually fairly low - even in the early eighties we were working on 10-18GHz. It is probably low enough for Si now-a-days (I've been out of the field for a while.)

The main issue at these sort of frequencies is parasitics, even a couple of mm of bondwires in a FET source can be enough to kill the gain (the rule of thumb we used to use was nH per mm).

You'll probably need to work on alumina rather than standard circuit boards if not working with MMICs. To do custom stuff would be expensive but perhaps commercial chips aimed at  WLAN might be ok.

My experience is not as relevant as that of radio hams who will know about doing things with materials available to amateurs rather than requiring multi-million pound clean room facilities.

HP have some very good app notes from the 70s/80s on amplifier design and S-parameters and so on - well worth reading.
« Last Edit: June 02, 2015, 08:01:42 pm by jpb »
 

Offline Lukas

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Re: How to amplify Super High Frequency signals?
« Reply #14 on: June 02, 2015, 11:00:54 pm »
If you don't know what transmission lines are, then it will be an extremely long and painful process to get anything working at GHz frequencies.

That doesn't matter. I'll take the time and I'm willing to learn.

Quote
What do you need it for? There are usually special amplifiers for many applications, which are geared towards the applications' requirements.

First a "simple" beacon, later a radar.
Take a look at http://hforsten.com/6-ghz-frequency-modulated-radar.html
 


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